In recent years, improvement of fuel economy is strongly required in automobiles against the background of environmental and resource problems. As a technology to realize this, hybrid vehicles with an electric power train system added to the powertrain system based on the conventional internal combustion engine are rapidly spreading.
An internal combustion engine, a motor generator, a high voltage battery, an inverter, a low voltage battery (14 V lead battery), a step-down DC/DC converter, and 14V electrical equipment and an ECU are assembled as a basic power train system of a hybrid vehicle.
Also, in order to improve fuel economy as much as possible, it is necessary to collect a lot of decelerating regenerative energy, the decelerating regenerative energy becomes high power in a short time, and cannot be accepted with a low voltage battery (14 V lead battery).
Also, the generated voltage of the motor generator is increased, a nickel metal hydride battery or a lithium ion battery, which is an electricity storage device good at rapid energy charging and discharging, is used as a high voltage battery, a power train system that adds a high voltage battery to a DC bus of an inverter are disclosed in Patent Literature 1.
[Patent Literature 1] JP2009-18719 A